Study on characteristics of noise-like pulses and dissipative soliton resonance pulses in nonlinear multimode interference mode-locked fiber lasers

Abstract

Nonlinear multimode interference mode-locking technology is a passive mode-locking technology utilized to generate ultrashort pulse lasers. This paper employs two sets of single mode fiber-graded-index multimode fiber-single mode fiber (SMF-GIMF-SMF) structures to create an SMF-GIMF-SMF-GIMF-SMF saturable absorber, which facilitates mode-locking; results in three distinct of pulse outputs: noise-like pulses, dissipative soliton resonance pulses, and dual-wavelength pulses. One of the SMF-GIMF-SMF structures is fixed, while the other is adjustable. The adjustable segment comprises two sections of SMF and one section of GIMF wound within a polarization controller (PC) at its center. By manipulating the PC, the mode-locking state can be modified. This paper explores the transition of soliton bunch pulses into noise-like pulses and successfully generates dissipative soliton resonance pulses in the anomalous dispersion region. Additionally, the filtering capability of the saturable absorber structure is leveraged to achieve dual-wavelength pulse output. The findings demonstrates that the mode-locking structure SMF-GIMF-SMF-GIMF-SMF formed by the series connection of two SMF-GIMF-SMF sets not only exhibits excellent saturable absorption characteristics conducive to ultrashort laser pulse mode-locking but can also be utilized for filtering to accomplish dual-wavelength output. Furthermore, through the adjustment of the PC and pump power during experiments, intricate nonlinear effects were induced, leading to a diverse range of mode-locking phenomena. This paper serves as a reference for theoretical research, performance enhancement, and practical applications of ultrafast fiber lasers.